The advent of recombinant DNA technology created the ability to alter the genetic makeup of organisms, eliminating the natural barriers that prevented transmission of genetic material between unrelated organisms. The ease of growing and manipulating bacteria and the numerous techniques available for introducing heterologous genes makes bacteria model organisms for genetic manipulation using recombinant DNA technology. Gram-negative and Gram-positive bacteria have been subjected to successful manipulation with recombinant DNA technology. Because of the well developed technology for transforming bacterial cells, the relative ease of genetically manipulating different bacteria, short reproduction times, and the comparatively small genomes, bacteria have been used as vehicles for synthetic biology applications, which aims to create novel artificial biological pathways, organisms or devices, or the redesign of existing natural biological systems. Moreover, bacteria exist with a wide range of functionalities, such as unique metabolic pathways (e.g., photo- and chemoautotrophism), magnetotactic properties (Blakemore, R., “Magnetotactic bacteria,” Science 24: 377-379, 1975), and extremophiles (e.g., thermophiles), which allows creation of recombinant bacteria with the properties present in the bacterial host cell.
Recombinant DNA techniques have also been used to manipulate the genetic makeup of eukaryotic cells, transiently or as a heritable property. For example, homologous and targeted recombination allows the generation of recombinant animals containing heterologous genes. Despite the advances in technology, manipulation of eukaryotic cells by recombinant DNA techniques has greater challenges as compared to manipulation of bacteria. Some eukaryotic cells targeted for recombinant DNA manipulation, e.g., mammalian cells, are slower to grow than bacterial cells, making selection of eukaryotic cells containing a heterologous nucleic acid more time consuming. Creation of eukaryotic cells containing longer lasting changes, including heritable changes, typically requires the use of homologous recombination, which despite the advances in technology, continue to have low efficiency rates. In addition, introduction of multiple, different heterologous nucleic acids is complicated by the higher complexity of eukaryotic cells (e.g., presence of organelles), greater degree of unpredictability in responses to multiple heterologous factors, and the technological disadvantages of selecting eukaryotic cells having multiple genetic/phenotypic changes. Thus, it is desirable to find alternative methods of engineering eukaryotic cells for introducing new functionalities into the cells, where the methods can be applied independently of or in combination with recombinant DNA technology for modifying eukaryotic cells.